Photoluminescence and interface abruptness in InGaAsP/InGaAsP quantum wells

Quantum well (QW) structures consisting of InGaAsP wells and InGaAsP barriers grown by gas-source molecular beam epitaxy have been examined by low temperature photoluminescence (PL) in order to evaluate the contributions of compositional fluctuations in the quaternary alloy and of interface roughness to the PL linewidth. The well material was InGaAsP with a bandgap corresponding to a wavelength of 1.3 μm and the barrier material was InGaAsP of 1.15 μm. The theory for QW excitonic linewidths as a function of well thickness L_z due to fluctuations in alloy composition has been extended to include the case of the quaternary InGaAsP barrier. If the interfaces are atomically abrupt, the linewidth is dominated by compositional fluctuations in the well at large L_z and compositional fluctuations in the barrier at small L_z. The theory predicts a weak dependence of the linewidth on L_z since the composition of the well and barrier are similar. For rough heterointerfaces, the theory indicates the usual increase in linewidth with decreasing L_z. Photoluminescence measurements at 13K in arrays of single InGaAsP/InGaAsP QWs with L_z from 1.0 to 6.0 nm show only a weak variation of the full width at half maximum (FWHM) with L_z, in agreement with the theory for smooth interfaces. Furthermore, the lowest measured FWHM of 8.9 meV was found for a narrow well of L_z=1.8 nm, indicating the InGaAsP/InGaAsP interfaces are smooth and that the PL linewidth is dominated by compositional fluctuations.     

Interface structure in arsenide/phosphide heterostructun grown by gas-source MBE and low-pressure MOVPE

We have used cross-sectional scanning tunneling microscopy (STM) to study interface structure in arsenide/phosphide heterostructures grown by gas-source molecular beam epitaxy (GSMBE) and by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). High-resolution images of GSMBE samples consisting of GaAs interrupted at 200Å intervals with a 40 s P₂ flux reveal substantial, growth-temperature-dependent incorporation of phosphorus with nanometer-scale lateral variations in interface structure. STM images of InGaAs/InP multiple quantum well structures grown by LP-MOVPE show evidence of interface asymmetry and extensive atomic cross-incorporation at the interfaces. Data obtained by STM have been corroborated by high-resolution x-ray diffraction and reflection high-energy electron diffraction. Together, these studies provide direct information about nanometer-scale grading and lateral nonuniformity of arsenide/phosphide interfaces that can occur under these growth conditions.     

Deep level electronic structure of ZnSe/GaAs heterostructures

We performed 1—2 keVcathodoluminescence measurements and He-Ne and HeCd excited photoluminescence studies of ZnSe/GaAs( 100) heterostructures grown by molecular beam epitaxy. Our goal was to investigate the deep level electronic structure and its connection with the heterojunction band offsets. We observed novel deep level emission features at 0.8, 0.98, 1.14, and 1.3 eV which are characteristic of the ZnSe overlayer and independent in energy of overlayer thickness. The corresponding deep levels lie far below those of the near-bandedge features commonly used to characterize the ZnSe crystal quality. The relative intensity and spatial distribution of the deep level emission was found to be strongly affected by the Zn/Se atomic flux ratio employed during ZnSe growth. The same flux ratio has been shown to influence both the quality of the ZnSe overlayer and the band offset in ZnSe/GaAs heterojunctions. In heterostructures fabricated in Se-rich growth conditions, that minimize the valence band offset and the concentration of Se vacancies, the dominant deep level emission is at 1.3 eV. For heterostructures fabricated in Zn-rich growth conditions, emission by multiple levels at 0.88,0.98, and 1.14 eV dominates. The spectral energies and intensities of deep level transitions reported here provide a characteristic indicator of ZnSe epilayer stoichiometry and near-interface defect densities.     

Properties of lnAsxP1-x layer formed by P-As exchange reaction on (001)lnP surface exposed to As4 beam

The P-As exchange reaction on InP surface exposed to As₄ beam was studied using photoluminescence (PL) and x-ray diffraction measurements as well as ultra-high vacuum scanning tunneling microscopy observation. It was found that as high as 90–95% of P can be exchanged by As and that the average depth of exchange reaction increases with the increase of As exposure time, being as deep as 5.5 ML for a long exposure. The splitting of PL peak takes place when the reaction depth exceeds 2 ML and the number of the split subpeaks increases with the increase of As exposure time. The PL peak splitting originates from the fluctuation of well thickness, caused by formation of InAs islands for strain relief during the exchange reaction.     

(111)B-oriented AlAs/GaAs/AIAs double barrier resonant tunneling devices grown in a gas source molecular beam epitaxy system

We have studied the growth of (lll)B-oriented AlAs/GaAs/AIAs double barrier resonant tunneling structures in a gas source molecular beam epitaxy system. We investigate the current peak-to-valley ratios of the resonant tunneling structures grown on (lll)B GaAs substrates under the various growth conditions, such as III/V flux ratios, substrate temperature, growth interruption at the heterointerfaces, buffer or contact layers, etc. We demonstrate that, in contrast to previous reports, high quality heterostructures can be grown in a gas source system if certainIII/V flux ratio, substrate temperature, and misoriented substrate are used. We show that the As/Ga flux ratio plays the key role for the growth on the misoriented ( 111 )B GaAs substrate, and growth at extremely high temperatures is not beneficial to the negative differential resistance. We also show that, although inserting a growth interruption in the buffer layer is believed to be helpful to the surface morphology, it is detrimental to the current peak-to-valley ratio.     

InAs/GaAs自组装量子点结构的能带不连续量

为确定异质结界面带阶,结合光致发光(PL)谱和深能级瞬态谱(DLTS)测量结果,利用有效质量近似理论,计算得到了InAs/GaAs自组装量子点结构的能带不连续量,其中导带不连续量ΔEc＝0.97 eV,价带不连续量ΔEv＝0.14 eV.     

Gas source molecular beam epitaxy grown strained-Si films on step-graded relaxed Si1−xGex for MOS applications

Gas source molecular beam epitaxy has been employed for the growth of a high quality strained-Si layer on a completely relaxed step-graded Si_1−xGe_x buffer layer. As-grown strained-Si layers have been characterized using secondary ion mass spectroscopy, Rutherford backscattering spectroscopy, atomic force microscopy, and spectroscopic ellipsometry for the determination of composition, thickness, crystalline quality, and surface roughness. Heterojunction conduction and valence band offsets (ΔE_c, ΔE_υ) of strained-Si/SiGe heterostructure have been determined from measured threshold voltages of a strained-Si channel p-metal oxide semiconductor field effect transistor (MOSFET) fabricated using grown films. MOS capacitance-voltage profiling has been employed for the extraction of strained-Si layer thickness and apparent doping profile in the device.     

全固源分子束外延InAsP/InGaAsP多量子阱1.55μm激光器

利用新型全固源分子束外延技术 ,对 1 .5 5 μm波段的 In As P/ In Ga As P应变多量子阱结构的生长进行了研究。实验表明 ,较低的生长温度或较大的 / 束流比有利于提高应变多量子阱材料的结构质量 ,而生长温度对材料的光学特性有较大的影响。在此基础上生长了分别限制多量子阱激光器结构 ,制作的氧化物条形宽接触激光器实现了室温脉冲工作 ,激射波长为 1 5 63 nm,阈值电流密度为 1 .4k A/ cm2 。这是国际上首次基于全固源分子束外延的 1 .5 5 μm波段 In As P/ In Ga As P多量子阱激光器的报道     

利用全固态分子束外延方法在Ge(100)衬底上异质外延GaAs薄膜及相关特性表征

利用全固态分子束外延(MBE)方法在Ge(100)衬底上异质外延GaAs薄膜,并通过高能电子衍射(RHEED)、高分辨X射线衍射(XRD),原子力显微镜等手段研究了不同生长参数对外延层的影响.RHEED显示在较高的生长温度或较低的生长速率下,低温GaAs成核层呈现层状生长模式.同时降低生长温度和生长速率会使GaAs薄膜的XRD摇摆曲线半高宽(FWHM)减小,并降低外延层表面的粗糙度,这主要是由于衬底和外延薄膜之间的晶格失配度减小的结果.     

Characteristics and device applications of erbium doped III-V semiconductors grown by molecular beam epitaxy

We have studied the properties of molecular beam epitaxially (MBE)-grown Erdoped III-V semiconductors for optoelectronic applications. Optically excited Er³⁺ in insulating materials exhibits optical emission chiefly around 1.54 μm, in the range of minimum loss in silica fiber. It was thought, therefore, that an electrically pumped Er-doped semiconductor laser would find great applicability in fiber-optic communication systems. Exhaustive photoluminescence (PL) characterization was conducted on several of As-based III-V semiconductors doped with Er, on bulk as well as quantum-well structures. We did not observe any Errelated PL emission at 1.54 μm for any of the materials/structures studied, a phenomenon which renders impractical the realization of an Er-doped III-V semiconductor laser. Deep level transient spectroscopy studies were performed on GaAs and AlGaAs co-doped with Er and Si to investigate the presence of any Er-related deep levels. The lack of band-edge luminescence in the GaAs:Er films led us to perform carrier-lifetime measurements by electro-optic sampling of photoconductive transients generated in these films. We discovered lifetimes in the picosecond regime, tunable by varying the Er concentration in the films. We also found the films to be highly resistive, the resistivity increasing with increasing Er-concentration. Intensive structural characterization (double-crys-tal x-ray and transmission electron microscopy) performed by us on GaAs:Er epilayers indicates the presence of high-density nanometer-sized ErAs precipitates in MBE-grown GaAs:Er. These metallic nanoprecipitates probably form internal Schottky barriers within the GaAs matrix, which give rise to Shockley-Read-Hall recombination centers, thus accounting for both the high resistivities and the ultrashort carrier lifetimes. Optoelectronic devices fabricated included novel tunable (in terms of speed and responsivity) high-speed metal-semiconductor-metal (MSM) photodiodes made with GaAs:Er. Pseudomorphic AlGaAs/ InGaAs modulation doped field effect transistors (MODFETs) (for high-speed MSM-FET monolithically integrated optical photoreceivers) were also fabricated using a GaAs:Er buffer layer which substantially reduced backgating effects in these devices.     

Optical properties of InAs<Subscript>1−x</Subscript>N<Subscript>x</Subscript>/In<Subscript>0.53</Subscript>Ga<Subscript>0.47</Subscript>As single quantum wells grown by gas source molecular beam epitaxy

Optical properties of InAs_1−xN_x/In_0.53Ga_0.47As (hereafter, abbreviated as InAsN/InGaAs) single quantum wells (SQWs) grown on InP substrates by gas source molecular-beam epitaxy are studied using photoluminescence (PL) measurements. By comparing the low-temperature PL spectra of InAs/InGaAs and InAsN/InGaAs SQWs, InAs and InAsN phases are found to coexist in the InAsN layer. Such serious alloy inhomogeneities result in obvious exciton localization by potential irregularities. The blue shift of the PL peak after rapid thermal annealing (RTA) is found to originate mainly from As-N interdiffusion inside the well layer. According to the temperature-dependent PL results, uniformity of the InAsN layer can be effectively improved by RTA, and the exciton localization is, thus, relieved. Comparison of luminescence quenching and excitation-power-dependent PL behavior between the QWs with and without nitrogen content suggests that the quality of the QW is degraded by the introduction of nitrogen, and the degradation can only be partially recovered by post-growth RTA.     

High resistivity LT-In0.47Ga0.53P grown by gas source molecular beam epitaxy

Low-temperature (LT) growth of In_0.47Ga_0.53P was carried out in the temperature range from 200 to 260°C by gas source molecular beam epitaxy using solid Ga and In and precracked PH₃. The Hall measurements of the as-grown film showed a resistivity of ∼10⁶ Ω-cm at room temperature whereas the annealed film (at 600°C for 1 h) had at least three orders of magnitude higher resistivity. The Hall measurements, also, indicated activation energies of ∼0.5 and 0.8 eV for the asgrown and annealed samples, respectively. Double-crystal x-ray diffraction showed that the LT-InGaP films had ∼47% In composition. The angular separation, Δθ, between the GaAs substrate and the as-grown LT-InGaP film on (004) reflection was increased by 20 arc-s after annealing. In order to better understand the annealing effect, a LT-InGaP film was grown on an InGaP film grown at 480°C. While annealing did not have any effect on the HT-InGaP peak position, the LT-InGaP peak was shifted toward the HT-InGaP peak, indicating a decrease in the LT-InGaP lattice parameter. Cross-sectional transmission electron microscopy indicates the presence of phase separation in LT-InGaP films, manifested in the form of a “precipitate-like” microstructure. The analytical scanning transmission electron microscopy analysis of the LT-InGaP film revealed a group-V nonstoichiometric deviation of ∼0.5 at.% P. To our knowledge, this is the first report about the growth and characterization of LT-InGaP films.     

Low temperature grown be-doped InAIP band offset reduction layer to p-type ZnSe

To solve the difficulty of achieving low resistance ohmic contact to p-type ZnSe, the use of an intermediate p-type InAlP layer to p-type ZnSe as a valence band offset reduction layer is studied by gas source molecular beam epitaxy. It is found that hole concentrations as high as 2 × 10¹⁸ cm⁻³ are easily obtained for p-type InAlP layers grown on GaAs even at low temperature of 350°C, although a higher Be cell temperature is required than that for a 500°C grown p-type InAlP due to the decreased electrical activity of Be in InAlP. Despite the very high Be concentrations, the Be precipitation/segregation is not observed. It was difficult to obtain the same hole concentration of InAlP layers grown on ZnSe as that on GaAs. However, the insertion of only several monolayers of GaAs between ZnSe and InAlP makes it possible to avoid faceting growth of InAlP and to improve the electrical properties of Be-doped InAlP grown on ZnSe. These results suggest that the Be-doped InAlP layer can be used as an intermediate layer to form the low resistance ohmic contact to p-type ZnSe.     

InAs/GaAs系列量子点研究

为了获得波长长、均匀性好和发光效率高的量子点,采用分子束外延(MBE)技术和S-K应变自组装模式,在GaAs(100)衬底上研究生长了三种InAs量子点。采用MBE配备的RHEED确定了工艺参数:As压维持在1.33×10-5Pa;InAs量子点和In0.2Ga0.8As的生长温度为500℃;565℃生长50nmGaAs覆盖层。生长了垂直耦合量子点(InAs1.8ML/GaAs5nm/InAs1.8ML)、阱内量子点(In0.2Ga0.8As5nm/InAs2.4ML/In0.2Ga0.8As5nm)和柱状岛量子点(InAs分别生长1.9、1.7、1.5ML,停顿20s后,生长间隔层GaAs2nm)。测得对应的室温光致发光(PL)谱峰值波长分别为1.038、1.201、1.087μm,半峰宽为119.6、128.0、72.2nm、相对发光强度为0.034、0.153、0.29。根据PL谱的峰位、半峰宽和相对发光强与量子点波长、均匀性和发光效率的对应关系,可知量子点波长有不同程度的增加、均匀性越来越好、发光效率显著增强。     

Effects of Rapid Thermal Annealing on Optical Properties of GaInNAs/GaAs Single Quantum Well Grown by Plasma-Assisted Molecular Beam Epitaxy

The effects of Rapid Thermal Annealing (RTA) on the optical properties of GaInNAs/GaAs Single Quantum Well (SQW) grown by plasma-assisted molecular beam epitaxy are investigated. Ion removal magnets were applied to reduce the ion damage during the growth process and the optical properties of GaInNAs/GaAs SQW are remarkably improved.RTA was carried out at 650℃ and its effect was studied by the comparising the roomtemperature PhotoLuminescence (PL) spectra for the non ion-removed (grown without magnets) sample with for the ion-removed (grown with magnets) one. The more significant improvement of PL characteristics for non ion-removed GaInNAs/GaAs SQW after annealing (compared with those for ion-removed) indicates that the nonradiative centers removed by RTA at 650℃ are mainly originated from ion damage. After annealing the PL blue shift for non ionremoved GaInNAs/GaAs SQW is much larger than those for InGaAs/GaAs and ion-removed GaInNAs/GaAs SQW. It is found that the larger PL blue shift of GaInNAs/GaAs SQW is due to the defect-assisted In-Ga interdiffusion rather than defect-assisted N-As interdiffusion.     

Effects of Rapid Thermal Annealing on Optical Properties of GaInNAs/GaAs Single Quantum Well Grown by Plasma-Assisted Molecular Beam Epitaxy

The effects of Rapid Thermal Annealing (RTA) on the optical properties of GaInNAs/GaAs Single Quantum Well (SQW) grown by plasma assisted molecular beam epitaxy are investigated. Ion removal magnets were applied to reduce the ion damage during the growth process and the optical properties of GaInNAs/GaAs SQW are remarkably improved. RTA was carried out at 650℃ and its effect was studied by the comparising the room\|temperature PhotoLuminescence (PL) spectra for the non ion removed (grown without magnets) sample with for the ion removed (grown with magnets) one. The more significant improvement of PL characteristics for non ion removed GaInNAs/GaAs SQW after annealing (compared with those for ion removed) indicates that the nonradiative centers removed by RTA at 650℃ are mainly originated from ion damage. After annealing the PL blue shift for non ion removed GaInNAs/GaAs SQW is much larger than those for InGaAs/GaAs and ion removed GaInNAs/GaAs SQW. It is found that the larger PL blue shift of GaInNAs/GaAs SQW is due to the defect assisted In Ga interdiffusion rather than defect assisted N As interdiffusion.     

离子损伤对等离子体辅助分子束外延生长的 Ga NAs/ Ga As和Ga In NAs/ Ga As量子阱的影响

研究了离子损伤对等离子体辅助分子束外延生长的 Ga NAs/ Ga As和 Ga In NAs/ Ga As量子阱的影响 .研究表明离子损伤是影响 Ga NAs和 Ga In NAs量子阱质量的关键因素 .去离子磁场能有效地去除了等离子体活化产生的氮离子 .对于使用去离子磁场生长的 Ga NAs和 Ga In NAs量子阱样品 ,X射线衍射测量和 PL 谱测量都表明样品的质量被显著地提高 .Ga In As量子阱的 PL 强度已经提高到可以和同样条件下生长的 Ga In As量子阱相比较 .研究也表明使用的磁场强度越强 ,样品的光学质量提高越明显     

新结构InGaP/GaAs/InGaP DHBT生长及特性研究

设计并生长了一种新的InGaP/GaAs/InGaP DHBT结构材料,采用在基区和集电区之间插入n+-InGaP插入层结构,以解决InGaP/GaAs/InGaP DHBT集电结导带尖峰的电子阻挡效应问题。采用气态源分子束外延(GSMBE)技术,通过优化生长条件,获得了高质量外延材料,成功地生长出带有n+-InGaP插入层结构的GaAs基InGaP/GaAs/InGaP DHBT结构材料。采用常规的湿法腐蚀工艺,研制出发射极面积为100μm×100μm的新型结构InGaP/GaAs/InGaP DHBT器件。直流特性测试的结果表明,所设计的集电结带有n+-InGaP插入层的InGaP/GaAs/InGaP DHBT器件开启电压约为0.15V,反向击穿电压达到16V,与传统的单异质结InGaP/GaAs HBT相比,反向击穿电压提高了一倍,能够满足低损耗、较高功率器件与电路制作的要求。     

Optical properties and structure of InAs quantum dots in near-infrared band

The InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) are studied as a function of growth temperature at a specific InAs coverage of 2.7 ML. The QDs density is significantly reduced from 8.0 × 1010 to 5.0 × 109 cm-2 as the growth temperature increases from 480℃ to 520℃, while the average QDs diameter and height becomes larger. The effects of the growth temperature on the evolution of bimodal QDs are investigated by combining atomic force microscopy (AFM) and photoluminescence (PL). Results show that the formation of the bimodal QDs depends on the growth temperature: at a growth temperature of 480℃,large QDs result from the small QDs coalition; at a growth temperature of 535℃, the indium desorption and InAs segregation result in the formation of small QDs.     

Gas source molecular beam epitaxy growth of SrS:Ce for flat panel displays

SrS:Ce thin films have been grown by gas source molecular beam epitaxy (GSMBE). The growth conditions have been systematically investigated as a function of growth temperature, sulfur to strontium flux ratio, and cerium flux. Single crystal SrS and high quality SrS:Ce were successfully grown on GaAs and glass substrates, respectively, without post-annealing process at temperature as low as 600°C. It was found that the electroluminescence (EL) performance was greatly improved by addition of ZnS during the growth.